1. Field of the Invention
This invention relates to a new grade of maraging steel which has excellent properties and is inexpensive to manufacture.
2. Description of the Prior Art
There is known 18Ni (Grade 250) maraging steel having a high tensile strength of, say, 180 kg/mm.sup.2. This steel, as solution treated, is relatively soft and, therefore, easy to machine or work. In order to obtain a high tensile strength of 180 kg/mm.sup.2, it is sufficient to heat the solution treated steel to a temperature of, say, 500.degree. C. for aging. The steel as solution treated can be machined or worked into the shape of a final product, since its aging does not bring about any appreciable dimensional change or develop any appreciable strain. Despite its high tensile strength, the steel retains high toughness. This steel has, however, the disadvantage of being expensive to manufacture, since it contains large quantities of cobalt, nickel and molybdenum, as shown in TABLE 1.
TABLE 1 ______________________________________ Chemical composition of 18Ni (Grade 250) maraging steel (mass %) C Mn P S Si Ni Co Mo Ti Al ______________________________________ 0.03 0.10 0.010 0.010 0.10 17.0 7.0 4.6 0.3 0.05 max. max. max. max. max. to to to to to 19.0 8.5 5.2 0.5 0.15 ______________________________________